1. Field of the Invention
The present invention relates to packing, and specifically to braided packing of the type having a number of longitudinally extending core strands around which a number of braid strands are braided. The present invention also relates to a method for making a packing of this type.
2. Description of the Prior Art
In many types of machines, sealing and packing materials are required which are substantially corrosion resistant and heat resistant, and which also have a long service life. A particular need for such materials arises in the case of machinery stuffing boxes, for example, for packing a rotary shaft or a reciprocating rod or other moving element at a point where the shaft or rod or element extends through an opening into another part of the machine, the part of the machine into which the shaft or rod or element extends containing some type of fluid which must be held against escape. Braided packing has been found to be particularly useful for packing such a journal, the packing being used to surround the moving element so that movement of the element is permitted, by rubbing against the packing, but substantially no fluid is permitted to pass through the opening due to the presence of the packing.
Commercially available packing, such as products available from Chesterton International, generally include natural fibers such as flax, jute, cotton or others, or manmade fibers such as polytetraflorethyne (PTFE) fibers, which are spun and twisted into yarns, the yarns then being braided or twisted into packing or woven into packing fabrics. It is known to impregnate such packings with liquid lubricants, greases and other lubricating compounds in order to reduce the friction between the packing and the moving part, such lubricants also assisting in the sealing function. It is also known to armor such packing with various metals to further reduce friction as well as to provide a partial or full metallic wearing face for the moving parts.
A fibrous graphite packing is known, for example, from U.S. Pat. No. 3,646,846, formed by an elongated braid of strands of graphite filament yarn, the strands and the interstices therebetween thoroughly impregnated with finely yet divided fluorocarbon resins and solid lubricants having crystal layer lattice structures, such as graphite. A braiding machine for making such a packing is also known from this patent.
Another type of braided packing is disclosed in U.S. Pat. Nos. 4,333,380; 4,256,011 and 4,110,835, which is also of the type initially described in the form of strands braided around a number of longitudinally extending strands. In the packing disclosed in these patents, however, the overall packing product is provided with an exterior helical twist. Machines for making such a packing are also disclosed in these patents.